In a general mounting method, IC chips are sealed in a package made of plastics and so on and mounted on a circuit board. Bare chip mounting has recently been utilized which enables a sharp reduction in mounting area compared to such semiconductor package mounting.
The bare chip mounting, in which IC chips unsealed in a package are mounted on a circuit board, is classified into three types.    (1) Electrodes on the chips are wire-bonded to electrodes on the circuit board.    (2) The electrodes on the chips are connected to the electrodes on the circuit board via a film having leads.    (3) The IC chips are placed face down and connected directly to the circuit board.
The flip chip in (3) is face-down mounting. In this case, a circuit formation surface of each of the semiconductor chips is placed opposite a circuit formation surface of the circuit board. The semiconductor chip is then laid on top of the circuit board via bumps formed of metal such as gold (Au) so as to be electrically continuous with the circuit board. The wire bonding in (1) is face-up mounting. In this case, the circuit formation surface of the circuit board is placed opposite a surface of the semiconductor chip which is located opposite the circuit formation surface thereof. Thin metal wires are then drawn out from the resulting structure by wire bonding. Compared to the face up mounting, the face down mounting enables a size reduction and is commonly utilized.
In recent years, for improved functions, a method described in Japanese Patent Laid-Open No. 2004-23045 or the like has been utilized. That is, even when a double-side mounting structure is adopted which includes a circuit board and semiconductor chips mounted on the opposite surfaces of the circuit board, the bare chips are connected to the circuit board by face-down mounting in order to achieve a size reduction.